Current technology can simultaneously monitor the firing of well over fifty neurons. The corresponding cross correlation matrix has well over a thousand independent entries, generally distributed in a seemingly random fashion because of the complex interconnections within typical neural tissue. The trend in experimental neurophysiology is clearly towards even larger sets of data. We propose to develop software for multi-neuron extracellular electrophysiology recording that will provide the experimentalist with a near real-time display of the correlations in firing within such large groups of neurons. The PC based software will be placed in the typical laboratory equipment chain after signal amplification, conditioning, and spike sorting and receive its input via Ethernet or other standard bus. It will calculate (in near real-time) the correlation between all pairs of input spike trains, and them present a frequently updated display of the cross correlation matrix in such a way that highly correlated sub-sets of neurons within the group will be displayed prominently. The software will be used to study changes in composition and correlation levels in these subsets as experimental conditions are changed, as an experimental animal is trained, and to help guide the placement of the recording electrode. PROPOSED COMMERCIAL APPLICATION: This device will be marketed as a specialty research tool to the electrophysiology research community. It will be useful in any laboratory performing extracellular multineuron monitoring and it is anticipated that it will become an essential tool for the neuroscience investigator.